There is an ever-increasing demand for renewable biofuels and bioenergy products as an alternative to fossil fuels. Biofuels are currently produced from, for example, various cellulosic materials and sugar-based plants, including sugarcane, beets, corn, rice, potatoes (among others), as well as wood chips. While the process is straight forward, producing biofuels and bioenergy products from these materials is, overall, inefficient and expensive given the cost of the source materials, and tends to drive up the price of food. Further, the current raw material sources for production of biofuel will not be sufficient to meet the escalating demands.
The U.S. population generates around 8.6 million dry metric tons of sludge annually, that is, approximately 13 billion pounds (dry basis) of sludge. Disposal of this enormous amount of sludge without substantial impact on the environment is an ongoing challenge.
Moreover, in the United States approximately 230 million tons (dry matter) of animal waste (manure) are generated every year. Unsafe and improper disposal of decomposable animal waste causes substantial environmental pollution, including surface and groundwater contamination, odors, dust, and methane and ammonia emission. Processing and/or disposal of municipal, industrial, and farm sewage waste (e.g., sludge) is costly, and has an enormous impact on the environment as well as on the public health.
Candidatus Microthrix are deeply branching filamentous actinobacteria occurring at the water-air interface of biological wastewater treatment plants where they are often responsible for foaming and bulking Candidatus Microthrix are notoriously difficult to grow in culture owing to their slow growth rate and unique growth medium requirements. This has long-delayed study of their genetic content. FEMS Microbiology Reviews 29 (2005) 49-64. In wastewater treatment plants, however, Candidatus Microthrix rapidly dominate the environment based on a competitive advantage which is likely conferred by their uptake of long-chain-fatty-acids (LCFA) that are accumulated as neutral lipids under anaerobic conditions and converted into phospholipids for cell division under aerobic conditions.
Lipid storing organisms are useful for the production of biofuel. The stored lipids may be extracted and processed directly into, for example, biodiesel as in algae biofuels. Additionally, organisms with complex lipid storing mechanisms, such as Candidatus Microthrix, may possess novel lipid processing and storage enzymes that can be introduced into transformed organisms for the direct production of biofuel or biofuel precursors.
Alternatively, proteins associated with lipid processing and storage could be used to produce biofuels in vitro. Suitable enzymes for commercial production of biofuels that can assemble and process alkyl chains into biofuel or biofuel precursors have been difficult to isolate.
Methods and systems are needed for recovering valuable components of sewage sludge to help satisfy energy needs, while simultaneously reducing the impact of such waste on the environment and the health of the population. Therefore, there is a need to increase the lipid production and storage from sewage sludge with an organism or community of organisms to serve as a suitable feedstock for biofuels production. Additionally, the isolation of novel lipid storage and processing proteins, and the genes encoding them, is desirable.